1. Field of the Invention
The present invention relates to a guide vane assembly used in a last stage of a compressor having multiple stages.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Gas turbine engines include stationary guide vanes 12 and 16 (FIG. 1) located upstream of the rotary blades, the guide vanes redirect the gas stream flow in a most effective direction to act on the rotating blade. Each guide vane 12 and 16 include an outer shroud segment 10 and 14, in which the vanes are secured, and an inner shroud 18 that provides a gap (13,17) between a tip of the guide vane and the shroud. If this gap (13,17) is large, a large portion of the gas stream will flow through the gap and bypass the rotary blades, therefore decreasing the efficiency of the gas turbine engine. The gap decreases due to thermal loads on the shrouds and vanes.
A compressor in a gas turbine engine includes a plurality of stages followed by a diffuser. It is desirable for the compressed air flow leaving the last stage of the compressor to enter the diffuser without any flow separation. It is desirable to have a smooth air flow passing into the diffuser in order to maximize the benefit of the diffuser. One guide vane can be used for the last stage of the compressor to guide the flow into the diffuser, but the air flow is not smooth enough. Using a double guide vane assembly in which two guide vanes are arranged in series will smooth out the air flow from the compressor to prevent flow separation. However, it is difficult to design this type of guide vane assembly with respect to the gap between vane tips and inner shrouds to minimize the air gap with changes in gap spacing due to thermal growth due to high temperatures in the compressor.
Prior attempts to improve on this loss due to a large gap is to secure both guide vanes 22 and 24 to a common outer shroud segment 20, and secure the inner shroud 26 to the guide vane tips to create a gap-less flow path through the vanes (FIG. 2). However, this attempt proved to be difficult to tune the guide vane assembly, and difficult to meet the structural criteria.
The inventors of the present invention has discovered that the tandem guide vanes can be secured to a common outer shroud segment while each guide vane tip maintains a gap between the respective tip and the inner shroud, while also providing for a spring bias member acting on the outer shroud at a location downstream from the two vanes and in a direction radially inward.